Using a conditional lethal of Drosophila, ecdysone-1, in which development can be arrested at 29 degrees in the third larval instar, strains with increased larval longevity will be selected in which developmental competence is maintained. The genetic differences between the short-and long-lived strains will be investigated initially by substituting chromosomes between the short-lived and long-lived strains. Ultrastructural, physiological and biochemical comparisons will be made between short- and long-lived strains as a function of chronological and physiological aging. Particular emphasis will be placed on the identification of differences in the synthesis or properties of proteins with particular reference to non-histone chromosomal proteins, cell surface proteins and receptors for the steroid molting hormone ecdysone.